The Intertubes have buzzing with news of a new way to make plastic without using petroleum or petrochemicals. Based on artificial photosynthesis, the process uses sunlight and carbon dioxide to make the building blocks for renewable plastics as well as fuels, paints, and your favorite pharmaceuticals. It’s all helped along by the notorious bacteria E. coli and some other bacteria we never heard of before. Since this is CleanTechnica, we figured you’d like to know a little more about that mystery bug, too, so here goes.
Artificial Photosynthesis and E. coli
To be honest, we’ being a little unfair to the bacteria. E. coli is short for Escherichia coli, best known for its bad — and potentially lethal — behavior linked to contaminated food and water.
However, E. coli exists in a wide variety of strains, most of which are actually harmless. They’re beginning to pop up in renewable fuel and “green” chemical applications, and the one involved in the new artificial photosynthesis study is one of those.
The new study comes from a team at the University of California – Berkeley with the Lawrence Berkeley National Laboratory, which you can find it in the journal Nano-Letters under the title “Nanowire–Bacteria Hybrids for Unassisted Solar Carbon Dioxide Fixation to Value-Added Chemicals.”
The basic concept is to mimic natural photosynthesis, in which plants use solar energy to reduce carbon dioxide to acetate, a ubiquitous biochemical “building block.” In the second step, acetate is converted to more complex chemical precursors.
The artificial photosynthesis concept (sometimes referred to as “artificial leaf” or “bionic leaf“) has been gathering steam lately. Aside from producing renewable fuel and other products, you can use it to sequester waste carbon dioxide from industrial processes.
Here in the US, one recent development is a proposed new $75 million round of funding for an Energy Department project for making fuel out of sunlight, carbon dioxide, and water.
Two Bacteria Are Better Than One
The other bacteria in the new artificial photosynthesis study is Sporomusa ovata. The National Institutes of Health has been tracking it, but our excuse for not knowing anything about is that the genome for S. ovata was only sequenced a couple of years ago. Now that it has, we’ll all probably be hearing more about it.
The 2013 genome announcement launched right into the good stuff by noting that “S. ovata uses N-methyl compounds, primary alcohols, fatty acids, and H2 and CO2 as energy and carbon sources to produce acetate.”
The folks at Berkeley Lab have been all over S. ovata for artificial photosynthesis (our bad for missing their April 16 press release) through a connection with UC Berkeley’s Kavli Energy NanoSciences Institute.
The new process starts by harvesting sunlight with a nanostructure of wires made from silicon and titanium:
…When sunlight is absorbed, photo-excited electron−hole pairs are generated in the silicon and titanium oxide nanowires, which absorb different regions of the solar spectrum. The photo-generated electrons in the silicon will be passed onto bacteria for the CO2 reduction while the photo-generated holes in the titanium oxide split water molecules to make oxygen.
Nanowire “forest” for artificial photosynthesis.
The bacteria in this first step is S. ovata:
S. ovata is a great carbon dioxide catalyst as it makes acetate, a versatile chemical intermediate that can be used to manufacture a diverse array of useful chemicals. We were able to uniformly populate our nanowire array with S. ovata using buffered brackish water with trace vitamins as the only organic component.
E.coli makes itself useful in the second step, in which acetate is converted into other chemical precursors.
In terms of efficiency — including solar conversion efficiency — so far the results have been good for butanol, amorphadiene (a pharmaceutical precursor for an antimalarial drug), and the biodegradable plastic PHB.
Moving forward, the team will try to figure out how to combine the two bacteria into one integrated step.
Improving the solar conversion efficiency is another goal. Right now they’re at .38, which is “about the same” as a natural leaf.
That sounds pretty dismal but the team anticipates an improvement to three percent for their next-generation system. That’s getting closer to the team’s goal of 10 percent for a commercially viable system.
They better get a move on
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Image credits (top image is enhanced screenshot): Courtesy of Lawrence Berkeley National Laboratory.
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